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Alkenes alkyl nitronate intermolecular cycloadditions

Elsewhere, Heaney et al. (313-315) found that alkenyloximes (e.g., 285), may react in a number of ways including formation of cyclic nitrones by the 1,3-APT reaction (Scheme 1.60). The benzodiazepinone nitrones (286) formed by the intramolecular 1,3-APT will undergo an intermolecular dipolar cycloaddition reaction with an external dipolarophile to afford five,seven,six-membered tricyclic adducts (287). Alternatively, the oximes may equilibrate to the corresponding N—H nitrones (288) and undergo intramolecular cycloaddition with the alkenyl function to afford five,six,six-membered tricyclic isoxazolidine adducts (289, R = H see also Section 1.11.2). In the presence of an electron-deficient alkene such as methyl vinyl ketone, the nitrogen of oxime 285 may be alkylated via the acyclic version of the 1,3-APT reaction and thus afford the N-alkylated nitrone 290 and the corresponding adduct 291. In more recent work, they prepared the related pyrimidodiazepine N-oxides by oxime-alkene cyclization for subsequent cycloaddition reactions (316). Related nitrones have been prepared by a number of workers by the more familiar route of condensation with alkylhydroxylamines (Scheme 1.67, Section 1.11.3). [Pg.51]

The intermolecular alkylation of metallo nitronates with various alkyl halides is limited. The addition of methyl iodide to the silver salt of an aryl nitro-methane provides the corresponding methyl nitronate in moderate yield (Eq. 2.13) (150), which has also been extended to the silver salt of trinitromethane (Scheme 2.16) (151-153). However, in the case of primary halides, both O- and C-alkylation are observed. For secondary and tertiary halides, only O-alkylation is observed, but in low yields. Unfortunately, under the reaction conditions, the starting alkyl halide can undergo dehydrohalogenation to provide the corresponding alkene, which then undergoes [3+2] cycloaddition with the alkyl nitronate. [Pg.131]

The use of mediators to improve reactivity or selectivity in nitrone cycloaddition chemistry begins with the nitrone generation step. As is well known, the N-alkyla-tion of oximes provides one of the most direct and convenient synthetic routes to N-alkylated nitrones from readily available aldehydes and ketones. Electrophilic mediators have been employed to activate alkenes for N-alkylation, both in intramolecular and intermolecular reactions. They include activation of the internal alkene function by the action of (a) strong nonmetallic electrophiles such as phenyl-selenenyl sulfate (159), and (b) metallic catalysts such as Ag(I) (160) and Pd(II) ions... [Pg.795]


See also in sourсe #XX -- [ Pg.141 , Pg.142 , Pg.143 , Pg.144 ]

See also in sourсe #XX -- [ Pg.141 , Pg.142 , Pg.143 , Pg.144 ]




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Alkenes 2+2]cycloaddition

Alkenes alkylated

Alkenes intermolecular

Alkenes nitrones

Alkenes, cycloadditions

Alkyl 5+2] cycloaddition

Alkyl intermolecular cycloaddition

Alkyl nitronates

Alkyl nitronates alkylation

Alkyl nitronates cycloadditions

Alkyl nitronates intermolecular

Alkylation alkene

Intermolecular cycloadditions alkyl nitronates

Nitronates alkylation

Nitronates cycloadditions

Nitronates intermolecular

Nitronates intermolecular cycloadditions

Nitrone-alkene cycloaddition

Nitrones cycloaddition

Nitrones nitrone-alkene

Nitrones, cycloadditions

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